[Arran]

Kirk;
This is much ado about nothing. The 10-S-464s have 6X5 problems because the engineers over at brand Z decided to ignore the specs in the RCA or Sylvania tube manual that states that the maximum current rating of a 6X5 was 70 ma, and whatever the maximum plate voltages were (they vary based on load and what the input filter is). They thought that they could get around it if they used pairs of 6X5s with the diodes wired in parallel rather then using an #80 or a 5Z3. In something like a five or six tube radio, with a 6K6 output tube, or a wire recorder, or a record player, there was never a problem with using a 6X5/6X5G/6X5GT, but connecting them as they did in a 10 tube radio with push pull 6V6s was just asking for trouble.
Depending on the year or production run, Philco used either type 84s or 6X5s in the power supplies of their 40-180, 41-280, 42-380 series chassis with few problems, the reason being is that they kept the B+ voltage down around 180 volts and used either #41s or 6K6s for power output tubes, which incidentally were designed for car radio use as well.
Regards
Arran